Steve Thomforde knows his trees.

After studying ecology for more than 10 years at the University of Wisconsin-Madison, he can spot the pokey limbs of an oak tree from about a mile away.

"I love oak trees," Thomforde says with a chuckle.

So much so that on Arbor Day, Thomforde helped about 200 volunteers plant 3,000 oaks in a 265-acre natural greenway along the border of Woodbury and Cottage Grove.

"We're some of these passionate people, 'Oh, I have to save the planet!' you know," said Thomforde, who is an ecologist and project manager for the nonprofit Great River Greening group, which organized the planting.

For nearly four hours, volunteers from age 4 and up trudged through tall-grassy prairie to several sites where they raked grass, shoveled soil and planted seedlings, which resembled twigs about the size of a pencil. The twigs came from a local nursery, which had cultivated hundreds of acorns that the group had gathered last year.

Of the 3,000 seedlings planted, the group hopes more than a third will grow, said Sandi Wagner, a volunteer supervisor who's been with the organization for two years.

The trees won't be visible for about 15 to 20 years, but those that take hold could live for hundreds of years, Wagner said.

For Thomforde, each tree not only plays an important role in an ecosystem, but tells its own story.

"I put my hand on the tree, and one day [think] 40,000 passenger pigeons sat on this limb alone [or] I had 17 baby calf elk growing in my shade over the past 500 years. It's like, that is so cool, man!" he said. "Each oak tree in your neighborhood can tell you a different story like that."

Volunteers marked the small trees with biodegradable blue tape to ensure that they can be seen. Nearby, and all across the prairie were orange tape markings of twigs planted last year, Wagner said.

The Great River Greening organization, which celebrated its 20-year anniversary on Arbor Day, engages thousands of volunteers each year to remove invasive species and plant rain gardens, trees and shrubs in the metro area and beyond.

"People like getting their hands dirty out here and knowing they're planting trees — especially trees, because that's something that's lasting," said Jen Kader, the organization's volunteer and outreach manager. "That's something that you think about."

Mary Kay Peterson of Lake Elmo said she participates in the plantings because she opposes the development and "jackhammering" of green spaces in the area, and decided to do something about it.

"We have to give back," she said.

Other Arbor Day volunteers brought friends or relatives.

Marissa Iacono from Maplewood brought her son Lucas, 4, and daughter Danielle, 7 weeks old. Not only did the day give Iacono a chance to give something back, it also gave her the opportunity "to expose my kids to conserving the environment, as well."

Said Deborah Karasov, the organization's executive director, "We are truly nurturing the stewards of our future."

Blair Emerson is a University of Minnesota student reporter on assignment for the Star Tribune